When Gennotte and Leland set the parameters of their model to values roughly corresponding to the U.S. stock market in 1987, the effects of whether or not 7t(po) is observed were dramatic. "The unobserved hedging which created a 30 percent crash in market prices, would have less than a 1 percent impact on prices if it were observed by all investors" (Gennotte and Leland 1990, p. 1016).

Donald MacKenzie, An Engine, Not a Camera, loc. 870